So what: Given how badly the results missed expectations, skepticism is naturally growing among investors over whether the drug will ultimately achieve regulatory approval. Wall Street had estimated that an oral version of treprostinal could potentially drive peak sales of about $750 million, higher than United Therapeutics' sales figure from all of last year, so it's no surprise that the shares are crashing as Mr. Market significantly lowers his growth expectations.

Now what: I'd look into this drop as possible buying opportunity. Given oral treprostinal's success in another trial and the fact that it is already approved in injectable and inhalable forms, management remains upbeat about the drug's prospects. While the chances of approval in late 2012 to early 2013 are certainly lower after today's news, United Therapeutics' stock price -- down 40% over the past three months alone and currently sporting a forward P/E of 12 -- might actually be safer after today's plunge.